Got some time to experiment with the clipping section and replaced the 4 diodes with two ZTX transistors (and two jumpers to keep the signal flowing) and there's a dramatic change in noise. It wasn't particularly noisy before but now it's dead quiet, even on max gain. It did lose some of the sharpness, but I actually prefer it this way. Stock pedal doesn't sound very tube amp-like to me, it's a bit harsh. With ZTX there's plenty of bite left but it's a bit more manageable.

I left sockets for LED diodes as well, so I might experiment with them, maybe replace them with a germanium diode + a MOSFET to smooth up things even further.

One more update - experimented with replacing LED clippers. Started with LED 3 and 4 after U2.2, as those were glowing brighter when playing compared the the other two...I'm assuming those are clipping the signal harder and playing with them would have a bigger impact. So I replaced them with a BS250 MOSFET (wired as S -> D+G) in series with a germanium diode to polarize it. The MOSFET has a forward voltage drop around 1.9V (0.6V in the opposite direction from the internal diode), so combined with a Ge diode, it comes up to around 2.1V. Red LEDs I have drop around 2V, so the clipping threshold is not all that different, but MOSFET clips very differently compared to the LED. LED has some hard, harsh quality to it that I don't particularly enjoy, especially with two LED clippers in the circuit MOSFET brought the distortion level down a little bit (which is not necessarily bad) reduced the buzzy overtones and made it a little bit more amp like.

Listening soundcloud clips back, there's no that much difference between them but in real life I can definitely hear the difference. So far, this combination of clippers sounds the best to me. LED in the first stage, ZTX in the second and MOSFET+Ge in the 3rd stage.

did you experiment with one diode + the ZTX in series instead of two diodes? I measured the ZTX and forward voltage is about the same as silicon diodes (~620mV), so if we use only one pair of ZTX devices, we'll effectively halve the headroom compared to the stock circuit. I tried the combination of Si diode and ZTX today and it's about halfway between the two versions...not bad at all.

bancika wrote:@bajamandid you experiment with one diode + the ZTX in series instead of two diodes? I measured the ZTX and forward voltage is about the same as silicon diodes (~620mV), so if we use only one pair of ZTX devices, we'll effectively halve the headroom compared to the stock circuit. I tried the combination of Si diode and ZTX today and it's about halfway between the two versions...not bad at all.Cheers

No, i had not tried that but I just ran a sim with a 1N4148 in series with ZTX951 and it showed the same response as two 1N4148. The sim for two ZTX951 in series shows a slight +2db broad boost around 600Hz however. I will give some of your suggested mods a try.cheersbajaman

I built my second BE-OD last week with Bugg's PCB. This time I left the second pair of LEDs out as per Bajaman's suggestion and I find the reduction in dirt to be quite noticeable. There is still plenty though! Actually it's an interesting sound because it's less harsh now. I also used silver mica for the pF values, and used a 470pF instead of the 120. My first pedal I also used 470pF but in ceramic, and used the full complement of LEDs. It's dirtier and a touch harsher.

I may stick some 1N4148s where the LEDs were left out as I usually have good results with them. I suspect LEDs were originally chosen because they seem to have that smooth, buttery sound that so many like - I generally prefer the spikier sound of 4148s.

FWIW I tested both pedals with gain on full and the trimmer up full - I'm not getting any oscillation with either. And I can't see why anyone would want to use the pedal like that - it's, um, not very subtle! You get a super-distorted sound way before you get to full. I keep the trimmer on lowest. Way more gain still than I ever need!

The trimmer is a very useful way to balance the ratio of clipping diodes (or ZTX transistors etc) in the feedback loop and the reversed pair of parallel red leds following this stage.With the trimmer set to lowest you should hear more "dirt' from the diode / transistors and less from the red leds and with it set to full the red leds will saturate well before the feedback diode stage.i suspect that it was friedman 's intention to adjust this trimmer to set this ratio of feedback to shunt clipping for the most realistic amp sound cheersbajaman

I also keep the trimmer gain at the lowest. Since, at this setting, the gain of this stage is -1, we can eliminate it. For educational purposes, let's also (properly) remove the op-amp that creates the active Vref supply and and only use the capacitively filtered resistive divider:

The Be-ODD Junior?

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Hey Bancika - really? I guess I've only ever tried LEDs where they have been chosen for their reduced high end or whatever it is that makes them sound like they do. It's really interesting how different diodes can sound - it's actually quite subtle but to us tone geeks they really make a difference.

Have to say I'm generally not a huge fan of LED clipping. It seems a bit too unsubtle or something - 1N4148s can at least sound a bit clearer. But I do play at the lower gain end of the spectrum.

FWIW I like to do some chip swapping. I don't do that stupid chip stacking, I just swap known good sounding dual op amps. With some circuits, like heavily modded/gained out TS808's, I hear a lot of difference with different chips. I play palm muted chunky Metal/Punk, and with that style the differences are apparent. Single note lead stuff or clean picking often sounds the same, I like to hit some gainy big chords so that there's some harmonic information to help make a judgement. When playing with a heavy palm mute and a lot of gain when A/B-ing chips, I hear differences in the tightness, amount of high/mid/low, etc. Try it sometime guys![/quote]

Just sounds like spending more money on something that won't make a difference for most people. Depends on how you play. I play chunk palm muted etc and never had any problems.[/quote]

Hey, if all IC's sound the same to you its all good. I guess you'll save some time/money, but IC's are very cheap from Mouser or Small Bear. The most expensive one I can think of is a Burr-Brown 2134 at a whopping $4 or so. 4558's and TL072's from various manufacturers are under a buck. In some positions/circuits the IC type makes little difference, in others they make a lot IMO.

The same concept and A/B test works with tubes as well. I like to dick around with V1 in high gain amps and a few different sets of whatever power tube is used. The differences in tubes can be subtle in something like a Blackface Twin Reverb, but are there nevertheless. The thing with an old BF Twin is that they sound great with any old tubes.

Anyway, off on a tangent there. Experiment if it suits you. This BEOD project presents some interesting opportunities for parts selection and swapping. The original pedal appears to use whatever is cheap and easily available. No disrespect toward Mr. F, just calling it how I see it. It seems the sound is in the CIRCUIT, not MAGIC NOS IC's, germanium, etc. In some pedals, guys obsess over carbon comp vs. metal film resistors, cap type, etc. In the BEOD, the resistors are SMD metal film (?), most of the caps are cheap polyester box film, diodes are generic SMD. Not much opportunity for parts snobbery there, lol. I used one of Bugg's boards and what I would say are superior quality parts. Maybe mine will sound better than the original! I will report back if IC changes make an audible difference in this pedal.

Random observation for FSB: It seems odd that that one 120pf cap is a good quality CDE (mica?) while many of the rest are SMD. Were there no SMD 120pf caps? Is that such a critical position in circuit that SMD would not do? Doesn't seem like it.

....The original pedal appears to use whatever is cheap and easily available. No disrespect toward Mr. F, just calling it how I see it. It seems the sound is in the CIRCUIT, not MAGIC NOS IC's, germanium, etc. In some pedals, guys obsess over carbon comp vs. metal film resistors, cap type, etc. In the BEOD, the resistors are SMD metal film (?), most of the caps are cheap polyester box film, diodes are generic SMD. Not much opportunity for parts snobbery there, lol.....

What you described is usually called "good design". Like with the (old) Rockman designs, it was questionable what could be "improved upon" with random part-swapping.

I went through all the pages, and hearing the clips, I'm eager to build the BE OD.

So, the original diodes are BAT54 or BAV99 ?For start, think I'll try Bajaman's (love the nick btw, and all the variants of it on the topic!) ZTX transistor connected as diode for clipping.Any non SMT replacement for the Schottky's from the original pedal?

Though I'm not interested anything similar to what the usual youtube clips provide, but I like the note definition of the pedal, seems promising.

OT: anybody seen the video of the Friedman JJ amp presented by Jerry Cantrell? Holy crap, that thing has plenty of gain on tap, and still excellent note definition!

Hi everybody, here is my take on the pcb for this project, still unverified.Single sided pcb with SMD IC's and clipping diodes and pcb mounted pots, should fit in a hammond b enclosure.Etching and soldering this board can be a little tricky for beginners.

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HiI built this version and it works perfectly. I didn't have BAV99 so just used a couple of 1n4148 smd that I had in stock. No oscillation either. I would post a photo of my pcb build for reference but have forgotten how to do it.Thank you.